1. Field of the Invention
The present invention relates to a network terminator and, more particularly, to a network terminator for connection to a digital broadcast system.
2. Description of the Related Art
The advent of digital television services offers the possibility of delivering interactive as well as broadcast services into the home. Various delivery methods to the home are being deployed, such as the Multipoint Video Delivery System (MVDS). Each home in the MVDS network would have a bidirectional microwave link to the head end for high bandwidth communication which will be in the 40.5-42.5 Ghz band. Networks would consist of multiple cells up to 4 kilometres diameter which are served by a head end. These areas could co-exist with cabled regions or be used where it is considered too expensive to cable in order that operators can extend their service areas.
Digital TV services may be broadcast in the format of a transport stream for instance as specified by DVB (EN 301 199, Digital Video Broadcasting; DVB Interaction Channel for LMDS Distribution System). This stream may include multiple program channels and other information. In this regard, a Forward Interaction path (downstream) may consist of control and interactive data interleaved with the program material. Furthermore, a Return Interaction path (upstream) may be provided using a 50 MHz block at the edge of the main downstream frequency range to convey user application data and responses to control messages.
The present application recognises for the first time that such digital broadcast systems, in allowing the transmission of various services and formats effectively simultaneously, present the user with a problem in making use of the services. In particular, there is no way in which a user can make use of the digital broadcast system for telephony at the same time as connecting a computer data interface.
According to the present invention, there is provided a network terminator for connection to a digital broadcast system, the network terminator including a front end for receiving downstream data packets and having a Medium Access Control unit for transmitting upstream data, a processor having at least one data interface, the processor distinguishing data protocols so as to route appropriate received data packets to the data interface and having an ATM segmentation unit for preparing ATM cells for transmission by the front end and a telephony unit for connection to at least one analog telephone line and for converting analogue speech signals to/from digital packets, wherein the processor routes appropriate received data packets to the telephony unit and prepares ATM cells from digital packets from the telephony unit for transmission by the front end.
In this way, the processor can distinguish data packets of different types and re-route them accordingly. A user may connect a telephone together with at least one other data interface and both the telephone and the data interface may make use of the digital broadcast system at the same time and without the need of the user to switch between devices connected to the digital broadcast system.
Preferably, the processor includes a transport stream demultiplexer for demultiplexing data packets of different protocols in the data stream received by the front end. The processor may include data interfaces for various systems such as Ethernet or i.LINK.
The front end may include a QPSK demodulator and may be used for receiving MPEG transport stream packets on the QPSK modulated satellite IF frequency range and/or can include a QAM demodulator for use for instance on a dedicated cable network. Furthermore, the front end may include a QPSK modulator for upstream transmission.
The telephony unit may include a PSTN Line Interface which may be POTS or ISDN grade.